Liquid crystal display device comprising a first optical compensating member between the liquid crystal layer and one of the first and second polarizing layers

ABSTRACT

A liquid crystal display device includes first and second substrates with first and second polarizing layers, a liquid-crystal layer, a matrix-driven electrode group; and a rear-illuminating device. Between the first polarizing layer and the liquid-crystal layer, a first optical compensating member is disposed without a birefringent medium sandwiched between the liquid-crystal layer and the first optical compensating member, and the first optical compensating member is constructed so that when a refractive index thereof in a slow-axis direction in a plane parallel to the substrate is taken as n1, a refractive index in a fast-axis direction in the plane parallel to the substrate is taken as n2, and a refractive index in a thickness direction is taken as n3, the first optical compensating member satisfies n1≈n3&gt;n2, and a slow axis thereof in the plane parallel to the substrate is substantially vertical to an optical axis of the liquid-crystal layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 12/136,134, filed Jun. 10, 2008, now U.S. Pat. No. 8,077,277, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device havinga liquid-crystal layer sandwiched between one pair of substrates.

2. Description of the Related Art

In Patent Documents 1, 2, and 3 listed below, a scheme with comb-likeelectrodes provided on one substrate is proposed as a scheme in which anelectric field is applied to a liquid crystal on the substratehorizontally.

This scheme is hereinafter referred to as the horizontal field scheme orin-plane switching (IPS) mode. In this scheme, the liquid-crystalmolecules rotate in a parallel plane with respect primarily to thesubstrate. It is known, therefore, that a wide viewing angle can beobtained since, when the crystal is viewed obliquely, the difference inbirefringent index between the application of the electric field andnon-application thereof is insignificant.

At the same time, it is also seen that in the IPS mode, although changesin the birefringent index of the crystal itself are insignificant, thecharacteristics of polarizers cause light to leak when the crystal isviewed from the azimuthally oblique directions shifted from theabsorption axes of the polarizers. A scheme that employs retardationfilms to prevent such leakage of light from the oblique directions ofpolarizers is disclosed in Patent Document 4. In this document, however,although consideration is given to reducing the influence of the liquidcrystal in a vertical alignment (VA) mode by improving only the viewingangles of the polarizers, no description is given of compensating forthe influence of the liquid-crystal layer in the IPS mode.

In Patent Document 5, while a means for solving the problem that whitechanges in color according to the particular viewing direction isdisclosed, the improvement of black display characteristics is notdescribed.

Meanwhile, a configuration with a retardation film disposed inside oneof multiple polarizers in order to improve the viewing anglecharacteristics of black display is disclosed in Patent Document 6. Thisscheme also allows for the influence of the triacetylcellulose (TAC)disposed as a supporting base material on both sides of the polarizer.It has been found during the present inventors' studies, however, thatthe configuration with one phase compensator at one side does not merelycause black to sink sufficiently, but does not reduce changes in colordue to the wavelength dispersion of the liquid-crystal layer, either. Inaddition, the difference in phase compensation due to whether thealignment axis (slow axis) of the liquid-crystal molecules during blackdisplay is parallel or perpendicular to the absorption axis of thepolarizer at the incident side is not described in Patent Document 6.

In the known examples described above, the viewing angle characteristicsare discussed in terms of luminance characteristics only and no measuresagainst the color change are disclosed.

Furthermore, a configuration that includes substantially an opticallyisotropic supporting base material in one polarizer and a retardationfilm in another polarizer in order to improve the oblique luminancedisturbance and/or oblique color disturbance of black display isdisclosed in Patent Document 7. The present inventors have studied thisscheme to find that although the scheme makes it possible to eliminatethe influence of the wavelength dispersion of a liquid-crystal layer,the display device itself is not constructed to reduce changes in colordue to the wavelength dispersion of a retardation film.

-   Patent Document 1: JP-B-S63-21907-   Patent Document 2: JP-A-H09-80424-   Patent Document 3: JP-A-2001-056476-   Patent Document 4: JP-A-2001-350022-   Patent Document 5: Japanese Patent No. 3204182-   Patent Document 6: Japanese Patent No. 2982869-   Patent Document 7: JP-A-2005-208356-   Patent Document 8: JP-A-2005-3733-   Non-Patent Document 1: “Crystal Optics”, compiled by the Japan    Society of Applied Physics, KOUGAKU-KONWAKAI, published by Morikita    Publishing Co., Ltd., 1984, 1st Edition, 4th Print, Chapter 5, pp.    102-163-   Non-Patent Document 2: “Fundamental Engineering”, Gendaikougakusha,    1999, 3rd Edition, Chapter 4, p. 210-   Non-Patent Document 3: J. Opt. Soc. Am. paper entitled “Optical in    Stratified and Anisotropic Media: 4×4-Matrix Formulation”, written    by D. W. Berreman, 1972, Volume 62, No. 4, pp. 502-510

SUMMARY OF THE INVENTION

The problem to be solved is that a liquid crystal display device of anin-plane switching (IPS) mode that has liquid-crystal moleculeshomogeneously aligned during black display and controls transmission andcutoff of light by applying a horizontal electric field to theliquid-crystal molecules suffers a luminance disturbance and colordisturbance in an oblique direction.

The IPS mode employs homogeneously aligned liquid-crystal molecules andtwo polarizers arranged so that the absorption axis of one polarizerpointing in a vertical direction with respect to the front of a screenand the absorption axis of the other polarizer pointing in a horizontaldirection are orthogonalized. When the screen is viewed obliquely fromthe vertical and horizontal directions, the absorption axes of the twopolarizers take a positional relationship in which the absorption axesare orthogonal to each other. Black luminance can, therefore, besufficiently reduced since the homogeneously aligned liquid-crystalmolecules and the absorption axis of one polarizer are parallel. Incontrast to this, when the screen is viewed obliquely from a 45°azimuthal direction, since the angle formed between the absorption axesof the two polarizers shifts from 90°, transmitted light causesbirefringence and this, in turn, causes leakage light, thus makingsufficient reduction of black luminance impossible. Additionally, theamount of oblique leakage light differs according to wavelength and thisdifference causes a color disturbance. Accordingly, an object of thepresent invention is to provide means which, in order to obtainappropriate display characteristics at practically everyomni-directional angle during black display in the IPS mode, reducesboth an increase in luminance of the black display made when a screen isviewed from an oblique direction, and the color disturbance.

The present invention is a liquid crystal display device comprising: afirst substrate with a first polarizing layer at an incident side oflight; a second substrate with a second polarizing layer at an exit sideof the light; a liquid-crystal layer disposed between the firstsubstrate and the second substrate such that respective absorption axesof the polarizing layers on the first and second substrates aresubstantially vertical to each other (the smaller of two angles formedranges from 88° to 90°), such that liquid-crystal molecules aresubstantially parallel to the substrate (the smaller of two anglesformed ranges from 0° to 5°), and such that the liquid-crystal layeritself is substantially vertical or substantially parallel to theabsorption axis of the first polarizing layer (the smaller of two anglesformed ranges from 0° to 2°); a matrix-driven electrode group with onepair of electrodes arranged on a pixel-by-pixel basis at a side close tothe liquid-crystal layer, on either the first substrate or the secondsubstrate; and a rear-illuminating device; wherein, between the firstpolarizing layer and the liquid-crystal layer, an optical compensatingmember is disposed without a birefringent medium (having an opticalretardation value of at least 20 nm in a plane parallel to theassociated substrate or in a thickness direction of this substrate)sandwiched between the liquid-crystal layer and the optical compensatingmember, and wherein, when a refractive index of the optical compensatingmember in a slow-axis direction in the plane parallel to the substrateis taken as n1, a refractive index in a fast-axis direction in the planeparallel to the substrate is taken as n2, and a refractive index in thethickness direction is taken as n3, the optical compensating membersatisfies n1≈n3>n2 and a slow axis thereof in the plane parallel to thesubstrate is substantially vertical to an optical axis of theliquid-crystal layer.

Other means will be described in detail in embodiments.

In the liquid crystal display device of the present invention, it ispossible, by including polarizers, a liquid-crystal layer, and anoptical compensating member, in the device configuration, and definingrespective optical constants of each of these optical members, to lessenimpacts of the liquid-crystal layer and optical compensating memberunder an oblique field and to reduce black luminance and colordeterioration in an oblique direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent fromthe following description of embodiments with reference to theaccompanying drawings in which:

FIG. 1 is a configuration diagram showing an embodiment of a liquidcrystal display device of the present invention;

FIG. 2 is a configuration diagram showing another embodiment of a liquidcrystal display device of the present invention;

FIG. 3 is a configuration diagram showing yet another embodiment of aliquid crystal display device of the present invention;

FIG. 4 is a configuration diagram for explaining a liquid crystaldisplay device of the present invention;

FIG. 5 is a configuration diagram showing still another embodiment of aliquid crystal display device of the present invention;

FIG. 6 is a configuration diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 7 is a definition diagram explaining a liquid crystal displaydevice of the present invention;

FIG. 8 is a general Poincare ball representation for explaining a liquidcrystal display device of the present invention;

FIGS. 9A and 9B are conceptual diagrams for explaining a liquid crystaldisplay device of the present invention;

FIGS. 10A and 10B are Poincare ball representations for explaining aliquid crystal display device of the present invention;

FIGS. 11A and 11B are other Poincare ball representations for explaininga liquid crystal display device of the present invention;

FIGS. 12A and 12B are other Poincare all representations for explaininga liquid crystal display device of the present invention;

FIGS. 13A and 13B are other Poincare ball representations for explaininga liquid crystal display device of the present invention;

FIG. 14A is a configuration diagram of a liquid crystal display deviceaccording to the present invention, and FIG. 14B is a Poincare ballrepresentation for explaining the liquid crystal display device of FIG.14A;

FIG. 15 is a conceptual diagram shown to explain evaluation indices usedin the present invention;

FIG. 16 is another conceptual diagram shown to explain evaluationindices used in the present invention;

FIG. 17 is a characteristics diagram showing an embodiment of a liquidcrystal display device of the present invention;

FIG. 18 is a characteristics diagram showing another embodiment of aliquid crystal display device of the present invention;

FIG. 19 is a characteristics diagram showing yet another embodiment of aliquid crystal display device of the present invention;

FIG. 20 is a characteristics diagram showing still another embodiment ofa liquid crystal display device of the present invention;

FIG. 21 is a configuration diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 22 is a further Poincare ball representation for explaining aliquid crystal display device of the present invention;

FIG. 23 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 24 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 25 is a configuration diagram for showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 26 is a further Poincare ball representation for explaining aliquid crystal display device of the present invention;

FIG. 27 is a further Poincare ball representation for explaining aliquid crystal display device of the present invention;

FIG. 28 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 29 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 30 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 31 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 32 is a further Poincare ball representation for explaining aliquid crystal display device of the present invention;

FIG. 33 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention;

FIG. 34 is a characteristics diagram showing a further embodiment of aliquid crystal display device of the present invention; and

FIG. 35 is a further Poincare ball representation for explaining aliquid crystal display device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Details of the present invention are described below.

With the rise of liquid-crystal TVs, it is important how anon-self-luminous liquid crystal display device that uses the lightemitted from an illuminating device lets the light pass through duringwhite display, and how the display device cuts off the light duringblack display. The present invention concerns how, when a screen isviewed from an oblique direction, especially, during black display, bothluminance and color deterioration are to be reduced at the same time.

First, prior to description of why luminance increases and colordeteriorates during black display when light is viewed from obliquedirections, definitions are shown below using FIG. 7. When incidentlight 60 from the illuminating device enters, then the light ismodulated by a liquid-crystal element, and the light exits a displayscreen 10D, if a normal direction of the display screen 10D is taken as80N, a horizontal direction as 70H, a vertical direction as 70V, and aprojection direction of a viewing direction 80V with respect to thedisplay screen 10D, as 80A, an angle formed between the horizontaldirection 70H and 80A is denoted as an azimuthal angle 81 by φ, and anangle formed between the normal direction 80N and the viewing direction80V is denoted as a polar angle θ.

Next, the reason for leakage of light is considered below with the polarangle θ and azimuthal angle φ satisfying θ≈0°, φ≈0°, 180°±90°, for onepair of orthogonal polarizers. As shown in FIG. 9A, when absorption axes11BA and 12BA (or transmission axes 11BT and 12BT) of the two polarizersare orthogonalized, light that has entered from the normal direction ofthe polarizer located at an incident side is formed into linearlypolarized light by the polarizer at the incident side and then absorbedinto the polarizer at an exit side, thus making black display possible.Meanwhile, as shown in FIG. 9B, the light when viewed from obliquedirections (θ≈0°, φ≈0°, 180°±90°) has a component parallel to thetransmission axis of the polarizer at an opposite side. The light,therefore, is not completely cut off by the polarizer at the oppositeside, and the light leaks as a result. In addition, according to studiesof the present inventors, when a parallel-aligned liquid-crystal layeris disposed between the orthogonal polarizers, if an optical axis of theliquid-crystal layer is parallel to that of the polarizer at theincident side, the light is not affected by the liquid-crystal layer,but the optical axis thereof suffers a shift, or if the orthogonality ofthe two polarizers is disturbed, the light is affected by theliquid-crystal layer.

These polarized states can better be understood by using Poincare ballrepresentation. The Poincare ball representation is disclosed inNon-Patent Document 4. If Stokes parameters S0, S1, S2, and S3 areplotted in x-axis and y-axis directions on a plane vertical to atraveling direction of the light, respective electric field amplitudesare taken as Ex and Ey, and a relative phase difference between Ex andEy is defined as δ(=δy−δx), the Stokes parameters are represented byS0=<|Ex|2>+<|Ey|2>S1=<|Ex|2>−<|Ey|2>S2=<2ExEy cos δ>S3=<2ExEy sin δ>  (Numerical expression 1)and S0 ²=S1 ²+S2 ²+S3 ² holds for complete polarization. In addition,this relationship, when represented on a Poincare ball, can be expressedas in FIG. 8. That is to say, axes S1, S2, and S3 are taken as axes of aspatially orthogonal coordinate system, and a point S denoting apolarized state is positioned on a spherical surface with a radius ofstrength S0. When a point of a certain polarized state S is taken andthis point is represented using latitude La and longitude Lo, since S0²=S1 ²+S2 ²+S3 ² holds for complete polarization, if a ball with aradius 1 is considered, the following is obtained:S1=cos La cos LoS2=cos La sin LoS3=cos La   (Numerical expression 2)where, on the Poincare ball, clockwise polarized light is disposed on anupper hemisphere, counterclockwise polarized light on a lowerhemisphere, linearly polarized light at an equatorial position,rightward circularly polarized light at an upper polar position, andleftward circularly polarized light at a lower polar position.

When considered on the Poincare ball, the state of FIG. 9B can berepresented as in FIGS. 10A and 10B. FIGS. 10A, 10B apply when theazimuthal angle φ=45° and the polar angle θ=60°, FIG. 10A being adiagram that shows projection onto an S1-S3 surface, and FIG. 10B beinga diagram that shows projection onto an S1-S2 surface. A polarizationstate of the polarized-light transmission axis 11BT at the incident sideof the light is denoted as 200T, the linearly polarized light having apolarization component against the absorption axis 11BA, as 200A, thepolarized-light transmission axis 12BT at the exit side, as 201T, andthe linearly polarized light having a polarization component against theabsorption axis 12BA, as 201A. That is to say, a distance 311 between200T and 201A is equivalent to leakage of light. It can therefore beseen that the leakage light can be prevented by conducting a change 300from the polarization state of 200T into that of 201A.

While FIGS. 10A, 10B assume an ideal state only of a polarizing layer, anormal type of polarizer has a supporting base material on both sides ofa polarizing layer and the supporting base material is usually formedfrom triacetylcellulose (TAC). Since TAC has a birefringent property,when incident light from an oblique direction exits, the polarized statechanges. This change in the polarized state due to the birefringentmedium is represented on a Poincare ball by rotating the optical axis ofthe liquid-crystal layer through a required angle around an axisdetermined by data (azimuthal angle, viewing angle) relating to incidentlight. This rotation is based upon the gradient retardation thatrepresents the oblique birefringence determined by physicalcharacteristics data (refractive index, thickness) of the birefringentmedium and the data (azimuthal angle, viewing angle) relating to theincident light.

For the above reason, although vertical incidence is not affected by thepolarization state of the light, oblique incidence is affected by thesupporting base material and the oblique incident light changes inpolarization state. Changes in polarization states in the optical layerconfiguration shown in FIG. 4 are next considered. A polarizer isdisposed on both sides of a liquid-crystal layer 15, a supporting basematerial 11C is disposed inside the polarizer 11 at an incident side,and a supporting base material 12C is disposed inside the polarizer 12at an exit side. An optical axis 15S of the liquid-crystal layer 15 isdisposed vertically to an absorption axis 11BA of the incident-sidepolarizer 11, in parallel to a transmission axis 11BT thereof, inparallel to an absorption axis 12BA of the exit-side polarizer 12, andvertically to a transmission axis 12BT thereof. This scheme is called ane-mode. When the axes of the upper and lower polarizers are rotatedthrough 90°, that is, when the optical axis 15S of the liquid-crystallayer 15 is disposed in parallel to the absorption axis 11BA of theincident-side polarizer 11, vertically to the transmission axis 11BTthereof, vertically to the absorption axis 12BA of the exit-sidepolarizer 12, and in parallel to the transmission axis 12BT thereof,this scheme is called an o-mode. In addition, usually, supporting basematerials 11A and 12A are arranged outside polarizing layers 11B and12B, respectively, as shown in FIG. 1. In fact, however, the twosupporting base materials are omitted since both are unnecessary forconsiderations on polarization states.

Regarding the configuration shown in FIG. 4, changes in polarizationstates on a Poincare ball are considered below using FIG. 11A.Hereinafter, unless otherwise defined, considerations are conducted withall physical characteristics data taken as data of the light whosewavelength is 550 nm. Considering the light when viewed at the azimuthalangle φ of 45° and the polar angle θ of 60°, as in FIGS. 10A and 10B,allows one to see that the polarization state of the light which haspassed through the transmission axis 11BT of a polarizing layer 11B isdenoted by 200T and changed into a polarization state 202 by thesupporting base material 11C. Next, the polarization state 202 ischanged into a polarization state 203 by the liquid-crystal layer 15,which is indicated at 301. Furthermore, the polarization state 203 ischanged into a polarization state 204 by the supporting base material12C of the exit-side polarizer 12. At this time, 201A denotes thepolarization state that matches the absorption axis 12BA of theexit-side polarizing layer 12B, and the light leaks by a distance 310between the polarization states 204 and 201A.

Additionally, although 550-nm light was considered in FIG. 11A, since avisible-light region ranges from 380 to 780 nm, light with a wavelengthof 400-700 nm substantially equivalent to the wavelengths of visiblelight is next considered per FIG. 11B in connection with theconfiguration of FIG. 4. Considering the light when viewed at theazimuthal angle φ of 45° and the polar angle θ of 60°, as in FIGS. 10Aand 10B, allows one to see that the polarization state of the lightwhich has passed through the incident-side polarizing layer 11B isdenoted by 200T and changed into a polarization state 212 by thesupporting base material 11C. At this time, since a magnitude ofretardation differs according to a particular wavelength of the light,length of a line denoting the polarization state 212 indicates that thepolarization state is changed into a different one. Furthermore, thepolarization state is changed into a polarization state 213 having awavelength-dependent spread, by the liquid-crystal layer 15. At thistime, 201A denotes the polarization state that matches the absorptionaxis 12BA of the exit-side polarizing layer 12B. Also, the presentinventors found that the light leaks by the distance between thepolarization states 214 and 201A and that the leakage level of the lightdiffers according to wavelength. It can be understood, however, that thecolor deteriorates when viewed from oblique directions.

The present invention is described in further detail. A configuration ofthe liquid crystal display device of the invention is shown in FIG. 1.This liquid crystal display device includes: a first substrate 13 with afirst polarizer (incident-side polarizer 11) at an incident side oflight; a second substrate 14 with a second polarizing layer (exit-sidepolarizer 12) at an exit side of the light, a liquid-crystal layer 15disposed between the first substrate 13 and the second substrate 14 suchthat respective absorption axes of the polarizing layers on the firstand second substrates are substantially vertical to each other (thesmaller of two angles formed ranges from 88° to 90°), such thatliquid-crystal molecules are substantially parallel to the substrate(the smaller of two angles formed ranges from 0° to 5°), and such thatthe liquid-crystal layer itself is substantially vertical orsubstantially parallel to the absorption axis of the first polarizinglayer (the smaller of two angles formed ranges from 0° to 2°), and theliquid-crystal layer further being constructed such that when anelectric field is applied in a direction parallel to the firstsubstrate, the liquid-crystal molecules rotate in a plane parallel tothe first substrate; a matrix-driven electrode group with one pair ofelectrodes arranged on a pixel-by-pixel basis at a side close to theliquid-crystal layer, on either the first substrate or the secondsubstrate; and a rear-illuminating device.

The left of FIG. 1 shows an e-mode in which an optical axis of theliquid-crystal layer 15 is substantially vertical to the absorption axisof the incident-side polarizing layer 11. In this case, an opticalcompensating member 16 is held in sandwiched form between theliquid-crystal layer 15 and the incident-side polarizing layer 11 andalso functions as a supporting base material, while an opticalcompensating member 17 is held in sandwiched form between theliquid-crystal layer 15 and the exit-side polarizing layer 12 and alsofunctions as another supporting base material.

Although FIG. 1 includes polarizer supporting base materials 11A, 12Aand substrates 13, 14, these can be ignored when polarization states areconsidered. When these elements are omitted and an optical block diagramthat explicitly indicates slow-axis directions of each member in a planeparallel to a substrate is considered, the optical configuration can beas in FIG. 5. A method of using the optical compensating members 16 and17 to reduce the leakage light from oblique directions in such anoptical configuration is next considered.

Changes in polarization state are shown in FIGS. 12A and 12B using aPoincare ball. These figures assume that a slow-axis direction in theparallel substrate plane is parallel to an x-axis direction, that x- andy-axial refractive indices are taken as “nx” and “ny”, respectively, andthat a refractive index in a direction of thickness “dr” is taken as“nz”. Also, such a medium that satisfies the following expression ishereinafter called the negative “a-plate”:nx≈nz>ny   (Numerical expression 3)In addition, hereinafter, a retardation of the negative “a-plate” refersto a retardation of the parallel substrate plane.

Considering the light when viewed at the azimuthal angle φ of 45° andthe polar angle θ of 60° in FIG. 12A allows one to see that thepolarization state of the light which has passed through thetransmission axis 11BT of the polarizing layer 11B is denoted by 200Tand changed into a polarization state 516 by the optical compensatingmember 16, which is indicated at 416. Next, the polarization state 516is changed into a polarization state 515 by the liquid-crystal layer 15as if a history of the change 416 by the optical compensating member 16were traced back, which is indicated at 415. Furthermore, thepolarization state 515 is changed into the polarization state 201A bythe optical compensating member 17, which is indicated at 417.

Additionally, although 550-nm light was considered in FIG. 12A, sincethe visible-light region ranges from 380 to 780 nm, light with awavelength of 400-700 nm substantially equivalent to the wavelengths ofvisible light is next considered per FIG. 12B. Light that has beenchanged by the optical compensating member 16 has a spread due to thewavelength dispersion of the optical compensating member, as in apolarization state 616. Next, the light is further changed by theliquid-crystal layer 15, but as discussed above, this change follows achange path substantially equal to the above. Thus, when the light thathas been assigned a spread by the wavelength dispersion of the opticalcompensating member is changed into a polarization state 615, the spreadcomes to be crossed out by a wavelength dispersion of the liquid-crystallayer. A subsequent polarization state change into a polarization state617 by the optical compensating member 17 makes it possible todramatically suppress an oblique luminance disturbance and an obliquecolor disturbance.

The o-mode in the right of FIG. 1 is next considered. In the o-mode, asin the right of FIG. 1, the optical axis of the liquid-crystal layer 15is substantially parallel to the absorption axis of the incident-sidepolarizing layer 11. In this case, the optical compensating member 16 isheld in sandwiched form between the liquid-crystal layer 15 and theexit-side polarizing layer 12 and also functions as a supporting basematerial, while the optical compensating member 17 is held in sandwichedform between the liquid-crystal layer 15 and the incident-sidepolarizing layer 11 and also functions as another supporting basematerial.

The optical configuration is shown in FIG. 6. Polarization state changesin this case are shown in FIGS. 13A and 13B using a Poincare ball. Asshown in FIGS. 13A, 13B, in the o-mode, a polarization state of thelight which has passed through the transmission axis 11BT of thepolarizing layer 11B is denoted by 200T and undergoes a change 417 to bechanged into a polarization state 517 by the optical compensating member17. Next, the polarization state undergoes a change 415 to be changedinto a polarization state 515 by the liquid-crystal layer 15. Next, thepolarization state undergoes a change 416 into a point of thepolarization state 201A by the optical compensating member 16 as if ahistory of the change 415 by the liquid-crystal layer 15 were tracedback.

The above polarization state change process allows an oblique luminancedisturbance and an oblique color disturbance to be suppressed. Accordingto these studies, under an appropriate configuration, the viewing-anglecharacteristics during black display become substantially equal betweenthe o-mode and the e-mode.

As would be understandable from the discussion conducted so far herein,according to the present invention, even if the retardation of theliquid-crystal layer 15 and that of the optical compensating member 16are positive wavelength dispersion levels, an advantageous effect thatcounteracts both wavelength dispersion levels can be obtained, whichimproves viewing performance over that achievable using any of theconventional techniques.

This concept is further advanced. If the wavelength is expressed as λ,the azimuthal angle as φ, and the polar angle as θ, an optical designthat satisfies the following expression becomes optimal to obtain anideal result:ΔnLC(λ,φ,θ)dLC(θ)−Δn(λ,φ,θ)d(θ)=kλ(Δn=nx−ny)(k: Constant)   (Numerical expression 4)where ΔnLC(λ, φ, θ) denotes a difference between a refractive index ofextraordinary light and that of ordinary light, dLC(θ) denotesoptical-path length of the liquid-crystal layer 15, Δn(λ, φ, θ) denotesa difference between refractive indices nx, ny in the parallel substrateplane of the optical compensating member 16, and d(θ) denotesoptical-path length of the optical compensating member 16. In thismethod, selection of materials for the liquid crystal and the opticalcompensating member 16 becomes very important. In general, however, anoptimum balance between the optical constant and wavelength dispersionof the optical compensating member 16 is difficult to achieve bymaterials selection.

The following examples can be presented as methods close to the abovedesign guidelines. In Patent Document 7, the influence of theliquid-crystal layer which causes the largest wavelength dispersion ofthe refractive index in the optical configuration is eliminated, whereasthe influence of the optical compensating members remains unremoved.

It is known that as in Non-Patent Document 2, the wavelength dispersionof a refractive index can well be approximated using the empiricalformula called the Shellmeier's dispersion formula. A furtherapproximated version of the Shellmeier's dispersion formula is theCauthy's dispersion formula represented as follows:n=A+B/λ ² +C/λ ⁴   (Numerical expression 5)where A, B, and C are constants.

The wavelength dispersion of Δn of a polycarbonate (PC), a material fora general-purpose optical compensating member, is roughly represented asfollows:Δn=0.9+0.04/λ²+0.0008/λ⁴  (Numerical expression 6)The wavelength dispersion of Δn of this general-purpose opticalcompensating member makes differences in polarization state changeaccording to wavelength, hence causing changes in chromaticity. Incontrast to this, the liquid-crystal layer 15 and optical compensatingmember 16 studied herein take an optical configuration that counteractsthe above wavelength dispersion of the refractive index. Compared withsuch optical configuration influenced by the wavelength dispersion ofthe optical compensating member as in Patent Document 7, therefore, theoptical configuration in the present invention makes chromaticitychanges significantly suppressible.

The optical configuration of an e-mode, proposed as an example in PatentDocument 7, is shown in FIG. 14A, and polarization state changes of thelight having a wavelength of 400-700 nm substantially equivalent to avisible-light region is shown in FIG. 14B. In the optical configurationof Patent Document 7, the influence of the liquid-crystal layer 15 isalmost removable by using the optical compensating members 18 and 19,whereas the influence of the optical compensating members 18 and 19remains unremoved. When the polarization state of the light is changedby the optical compensating members 18, 19, the wavelength dispersionthereof assigns a spread to the polarization state, as in 618, 619,resulting in an oblique luminance disturbance and changes inchromaticity. In contrast to this, in the optical configuration studiedherein, differences in polarization state change at wavelengths of R, G,and B, are suppressed, as in FIG. 12B. A liquid crystal display devicesubstantially free from an oblique luminance disturbance and achromaticity change is thus realized.

For example, if, in a general liquid crystal display device with ared/green/blue tri-color filter, transmission peak wavelengths of thered, green, and blue regions of the color filter are taken as R, G, andB, respectively, thickness of a liquid-crystal layer 15 as dLCR, dLCG,dLCB, and thickness of an optical compensating member 16 as drR, drG,drB, a material of the optical compensating member is selected so thatthe following condition is satisfied:

$\begin{matrix}{{{\left. {{{{\Delta\;{{{nLC}(B)} \cdot {dLCB}}} - {{\left( {{n\; 1(B)} - {n\; 2(B)}} \right) \cdot {drB}}{/}\Delta\;{{{nLC}(G)} \cdot {dLCG}}} - {\left( {{n\; 1(G)} - {n\; 2(G)}} \right) \cdot {drG}}}} < {0.9 + {0.04/B^{2}} + {0.0008\;/B^{4}}}} \right)/\left( {0.9 + {0.04/G^{2}} + {0.0008/G^{4}}} \right)}{{{\Delta\;{{{nLC}(G)} \cdot {dLCG}}} - {{\left( {{n\; 1(G)} - {n\; 2(G)}} \right) \cdot {drG}}{/}\Delta\;{{{nLC}(R)} \cdot {dLCR}}} - {\left( {{n\; 1(R)} - {n\; 2(R)}} \right) \cdot {drR}}}}} < {\left( {0.9 + {0.04/G^{2}} + {0.0008/G^{4}}} \right)/\left( {0.9 + {0.04/R^{2}} + {0.0008/R^{4}}} \right)}} & \left( {{Numerical}\mspace{14mu}{expression}\mspace{14mu} 7} \right)\end{matrix}$This condition becomes particularly important for providing a widerrange of choices for the material of the optical compensating member.When an optical compensating member of a general material is used,merely employing the optical configuration studied herein makes itpossible to satisfy the condition defined by expression (7), and obtainoptical characteristics equivalent to or surpassing those described inPatent Document 7. However, desired optical characteristics may not beobtainable if a material with wavelength dispersion characteristicssignificantly different from those of a general material is used forwider selection of the materials usable as alternatives. In that case,it is possible to satisfy expression (7) by undertaking thecountermeasures described later herein.

For example, advantageous effects close to those of the above-describedoptical design can be developed by adjusting the retardation of theoptical compensating member 16 independently for each color region ofthe color filter. If this method is adopted, optical designing close tothat which satisfies expression (4) can be implemented using a conditionother than selecting a material.

Alternatively, advantageous effects close to those of theabove-described optical design can likewise be developed by changing thethickness of the liquid-crystal layer 15, that is, a cell gap, for eachcolor region of the color filter. For example, in a general liquidcrystal display device with a red/green/blue tri-color filter, ifthicknesses of a liquid-crystal layer 15 that are associated with thecolor filter components of red, green, and blue, are taken as dR, dG,and dB, respectively, the liquid-crystal layer 15 is so-called“multi-gapped” to satisfy the following condition:dR>dG>dB   (Numerical expression 8)If this method is adopted, an optical design creating a state close tosuch an ideal state that satisfies expression (4) can be achieved usinga condition other than defining optical constants.

Further detailed examples of the concepts discussed above are shown inthe embodiments below.

Embodiments

Content of the present invention is described in further detail below byshowing more specific examples of the invention. The embodiments belowrepresent specific examples of the present invention and do not limitthe invention. Study results derived from numeric calculations obtainedusing optical simulation based on the 4×4-matrix method disclosed inNon-Patent Document 3 are included in the embodiments. The simulationassumes a general configuration and is based on spectral characteristicsof a tri-wavelength cathode-ray tube used in a normal type of backlight,spectral transmission characteristics of a red/green/blue tri-colorfilter, and polarizing layer spectral characteristics of the 1224DUpolarizer manufactured by the Nitto Denko Corp. The above simulationalso assumes a nematic liquid crystal having a liquid-crystal layer,which contains liquid-crystal molecules whose extraordinary-lightrefractive index is 1.573 and whose ordinary-light refractive index is1.484, and the liquid-crystal layer is 3.9 μm thick. In addition, apolycarbonate(PC)-based, polystyrene-based, or norbornene-basedmaterial, or the like, or a liquid-crystalline high-molecular polymericmaterial is used for wavelength dispersion of optical compensatingmembers, but the invention is not limited to or by these materials.

The present invention also assumes disposing an optical compensatingmember between a first substrate and a second substrate, and thistechnique is disclosed in, for example, Patent Document 8 and others.According to the present inventors' studies, one of problems associatedwith such a technique exists in surface planarity. When an opticalcompensating member is disposed between the first substrate and thesecond substrate, if the optical compensating member has a roughsurface, this causes nonuniform liquid-crystal layer thickness, thusresulting in nonuniform in-plane display or in reduced contrast.According to the present inventors' studies, however, in the IPS modeusing such an electric fringe field as proposed in Patent Document 9,the nonuniformity of in-plane display or reduction in contrast due tothe nonuniformity of the liquid-crystal layer in thickness does noteasily occur, so the IPS mode with the above-mentioned fringe field canbe easily combined with the technique of disposing an opticalcompensating member between the first substrate and the secondsubstrate.

Additionally, since a current general configuration is described in theembodiments, the description assumes that one birefringent function isrealized for one optical compensating member, but birefringence of eachoptical compensating member shown in the embodiments may be realized bycombining a plurality of optical compensating members. For example,retardation may be adjusted by stacking optical compensating members.Alternatively, each optical compensating member and each polarizinglayer may be formed by coating the surface of the substrate with amaterial and then conducting an aligning process. In this case, however,the configuration shown in the particular embodiment may change. Morespecifically, the particular polarizing layer may be disposed at theliquid-crystal layer side of the substrate. Furthermore, while FIG. 1 isshown as a structural example in the embodiments, there is no problem,even if the structure shown in FIG. 2 or 3 is employed. The presentinvention places importance upon the optical configuration, and providedthat the optical configuration shown in the invention is realized,advantageous effects thereof can be attained, irrespective of a physicalconfiguration. For this reason, the optical configuration is shown inthe embodiments where appropriate.

The terms “vertical” and “90°” used in the embodiments do not mean acompletely vertical state, and re-reading these expressions to mean asubstantially vertical state or to mean that the smaller of two anglesformed between associated optical elements ranges from 88° to 90° doesnot affect the essence of the description. This also applies to otherterms such as “parallel”.

The liquid-crystal cells, electrode structures, substrates, polarizerlayers, and illumination device used in a conventional device of the IPSmode can be applied as they are. The present invention relates tospecifications and configurations of optical members.

The smaller of two angles of the liquid-crystal layer optical axis withrespect to the substrate under an electrically de-energized state of theliquid-crystal layer, that is, a pre-tilt angle is 0° in the simulationshown in the embodiments, but in a range of ±5, there is no significantdifference between tendencies shown in the embodiments. However, themost favorable characteristics of all those actually obtained areexhibited at the pre-tilt angle of 0°.

The terms used herein are next described. Optical compensating memberscan be considered as refractive index ellipsoids, and if the refractiveindices in the parallel substrate plane are defined as “nx”, “ny”, arefractive index having an axis in a direction vertical to the medium,as “nz”, and thickness of each optical compensating member, as “dr”,then the retardation Δnd in the parallel substrate plane that denotesbirefringence, retardation Rth in the thickness direction, and an Nzcoefficient are expressed as follows:Δnd=|(nx−ny)d|Rth=|((nx+ny)/2−nz)d|Nz=(nx−nz)/(ny−nz)   (Numerical expression 9)Hereinafter, unless otherwise defined for 0<Nz<1 in a biaxiallyanisotropic optical compensating member, the retardation refers to theretardation in the parallel substrate plane. In addition, unlessotherwise defined for Nz<0, 1<Nz, the retardation refers to theretardation Rth in the thickness direction.

Furthermore, a “substantially isotropic property” refers to that of amedium whose in-plane retardation and thickness-directional retardationare greater than 0 nm, but smaller than 20 nm. Other media arebirefringent media.

The kinds of birefringent media other than biaxially anisotropic opticalcompensating members include uniaxially anisotropic optical compensatingmembers. In the embodiments, a positive “a-plate”, a negative “a-plate”,a positive “c-plate”, and a negative “c-plate” are used, which aredescribed below.

-   Positive “a-plate”: nx>ny≈nz-   Negative “a-plate”: nx≈nz>ny-   Positive “c-plate”: nz>nx≈ny-   Negative “c-plate”: nx≈ny>nz    Hereinafter, unless otherwise defined, a retardation of the    “a-plate” refers to the retardation in the parallel substrate plane,    and a retardation of the “c-plate” refers to the retardation in the    thickness direction.

Moreover, although these uniaxially anisotropic optical compensatingmembers are used in the embodiments, it is not always necessary,according to the present inventors' studies, to use the positive“a-plate”, the negative “a-plate”, the positive “c-plate”, or thenegative “c-plate”. Therefore, there is no problem, even if the negative“a-plate” is considered to satisfy −0.3<Nz<0.3, the positive “a-plate”to satisfy 0.7<Nz<1.0, the positive “c-plate” to satisfy Nz<−5, or thenegative “c-plate” to satisfy Nz>5.

First Embodiment

A structure of a first embodiment is shown in the left of FIG. 1, and anoptical configuration of the e-mode, in FIG. 5. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical compensating member withan Nz coefficient smaller than 0 is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIGS. 12A and 12B. A polarizationstate of light which has passed through a transmission axis 11BT of apolarizing layer 11B is denoted by 200T and undergoes a change 416 to bechanged into a polarization state 516 by the optical compensating member16. Next, the polarization state undergoes a change 415 to be changedinto a polarization state 515 by a liquid-crystal layer 15 as if ahistory of the change 416 by the optical compensating member 16 weretraced back. The polarization state further undergoes a change 417 intoa polarization state 201A by the optical compensating member 17.

There is a need to define evaluation indices here. The present inventionis intended to reduce changes in luminance and color, associated withchanging a viewing angle during black display, so respective evaluationindices need to be introduced.

A maximum transmittance value achievable when the viewing angle ischanged is introduced as an index of changes in luminance. Thetransmittance here means that calculated with visible sensitivity at anincident-light wavelength of 400-700 nm taken into account. This is nextdescribed per FIG. 15. This figure shows evaluation results ontransmittance-viewing angle characteristics obtained at a fixedazimuthal angle and different polar angles during black display in threekinds of liquid crystal display devices different in specifications ofthe optical compensating members. It can be seen from FIG. 15 thatspecifications 3 provide the most favorable luminance changecharacteristics. In addition, comparisons between the maximumtransmittance values in the three kinds of specifications indicate thatsimilar results are obtained. Reference numerals 451T1, 451T2, and 451T3denote the maximum transmittance values of specifications 1,specifications 2, and specifications 3, respectively. As can be seenfrom these results, as the maximum transmittance value decreases,changes in luminance due to changes in viewing angle also decrease. Whensuch an optical compensating member as shown in FIG. 9 is not provided,the maximum transmittance value during black display is about 2%.

Next, Δu′v′ is introduced as an index of changes in chromaticity. Anexplanatory diagram is shown in FIG. 16. FIG. 16 is a u′v′chromaticity-plotted representation of the colors developed during blackdisplay in the configuration of FIG. 9, and all chromaticity coordinatesassociated with all azimuthal angles and all polar angles are plotted inthe figure. The elliptic region shown in FIG. 16 is consequentlyobtained. Reducing changes in chromaticity due to changes in the viewingangle is equivalent to downsizing the elliptic region of FIG. 16.Major-axis length of the ellipse is therefore adopted as an evaluationindex, and Δu′v′ is the index.

In contrast to this, maximum transmittances attained in the presentembodiment by changing the Nz coefficient and retardation value of theoptical compensating member 17 in a range from −3 to −1 and a range from40 to 150 nm, respectively, with the retardation value of the opticalcompensating member 16 fixed at 240 nm, are shown in FIG. 17, and Δu′v′,in FIG. 18. A maximum transmittance of 2% or below is obtained in aretardation range of 40-130 nm, and favorable viewing-anglecharacteristics are realized. In addition, when the Nz coefficient andretardation value of the optical compensating member 17 are −1.0 and 60nm, respectively, a maximum transmittance of 0.089% and a Δu′v′ value of0.14 are attained and particularly favorable results obtained. ThisΔu′v′ value is therefore applied in the present embodiment.

Furthermore, as discussed above, using the multi-gapping technique toindependently change each of the liquid-crystal layer thicknesses dR,dG, and dB associated with the color filter components of R (red), G(green), and B (blue), makes it possible to further reduce obliqueluminance changes and chromaticity changes, for example, if dR≧dG>dB.

Positionally inverse arrangement of the liquid-crystal layer 15 andoptical compensating member 16 in the optical configuration also yieldssubstantially the same results as those obtained in the e-mode.

Second Embodiment

A structure of a second embodiment is shown in the right of FIG. 1, andan optical configuration of the o-mode, in FIG. 6. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical compensating member withan Nz coefficient smaller than 0 is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIGS. 13A and 13B. A polarizationstate of light which has passed through a transmission axis 11BT of apolarizing layer 11B is denoted by 200T and undergoes a change 417 to bechanged into a polarization state 517 by the optical compensating member17. Next, the polarization state undergoes a change 415 to be changedinto a polarization state 515 by a liquid-crystal layer 15. Thepolarization state further undergoes a change 416 into a point of apolarization state 201A by the optical compensating member 16 as if ahistory of the change 415 by the liquid-crystal layer 15 were tracedback. In the present embodiment, a maximum transmittance of 2% or belowin the retardation range of 40-130 nm is attained and substantially thesame results as obtained in the e-mode of the first embodiment areobtained.

An optimum retardation value of the optical compensating member 16 andan optimum retardation value and optimum Nz coefficient of the opticalcompensating member 17 depend upon the retardation value of theliquid-crystal layer and upon wavelength dispersion characteristics ofthese optical members. Positionally inverse arrangement of theliquid-crystal layer 15 and optical compensating member 16 in theoptical configuration also yields substantially the same results asthose obtained in the e-mode of the first embodiment.

Third Embodiment

A structure of a third embodiment is shown in the left of FIG. 1, and anoptical configuration of the e-mode, in FIG. 5. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical phase-compensating filmwith an Nz coefficient greater than 0, but smaller than 1, is used as anoptical compensating member 17. This configuration also makes itpossible to achieve the polarization state changes shown in FIGS. 12Aand 12B. A polarization state of light which has passed through atransmission axis 11BT of a polarizing layer 11B is denoted by 200T andundergoes a change 416 to be channel into a polarization state 516 bythe optical compensating member 16. Next, the polarization stateundergoes a change 415 to be changed into a polarization state 515 by aliquid-crystal layer 15 as if a history of the change 416 by the opticalcompensating member 16 were traced back. The polarization state furtherundergoes a change 417 into a polarization state 201A by the opticalcompensating member 17.

Maximum transmittances attained in the present embodiment by changingthe Nz coefficient and retardation value of the optical compensatingmember 17 in a range from 0.2 to 0.8 and a range from 20 to 250 nm,respectively, with the retardation value of the optical compensatingmember 16 fixed at 300 nm, are shown in FIG. 19, and Δu′v′, in FIG. 20.A maximum transmittance of 2% or below is obtained in a retardationrange of 20-230 nm, and favorable viewing-angle characteristics arerealized. In addition, when the Nz coefficient and retardation value ofthe optical compensating member 17 are 0.4 and 150 nm, respectively, amaximum transmittance of 0.075% and a Δu′v′ value of 0.12 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore adopted in the present embodiment.

As can be seen from the polarization state changes in FIGS. 12A, 12B andfrom the results in FIGS. 19, 20, an optimum retardation value of theoptical compensating member 16 and an optimum Nz coefficient and optimumretardation value of the optical compensating member 17 depend upon theretardation value of the liquid-crystal layer and upon wavelengthdispersion characteristics of these optical members. In addition, theresults in the o-mode and the results obtained by positionally inversearrangement of the liquid-crystal layer 15 and optical compensatingmember 16 in the optical configuration are substantially the same asobtained in the e-mode.

Fourth Embodiment

A structure of a fourth embodiment is shown in the left of FIG. 1, andan optical configuration of the e-mode, in FIG. 21. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical compensating member withan Nz coefficient smaller than 0 is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIG. 22. A polarization state oflight which has passed through a transmission axis 11BT of a polarizinglayer 11B is denoted by 200T and undergoes a change 416 to be changedinto a polarization state 516 by the optical compensating member 16.Next, the polarization state undergoes a change 415 to be changed into apolarization state 515 by a liquid-crystal layer 15 as if a history ofthe change 416 by the optical compensating member 16 were traced back.The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17.

Maximum transmittances attained in the present embodiment by changingthe Nz coefficient and retardation value of the optical compensatingmember 17 in a range from −3 to −1 and a range from 40 to 250 nm,respectively, with the retardation value of the optical compensatingmember 16 fixed at 180 nm, are shown in FIG. 23, and Δu′v′, in FIG. 24.A maximum transmittance of 2% or below is obtained in a retardationrange of 40-200 nm, and favorable viewing-angle characteristics arerealized. In addition, when the Nz coefficient and retardation value ofthe optical compensating member 17 are −1.0 and 135 nm, respectively, amaximum transmittance of 0.090% and a Δu′v′ value of 0.15 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore applied in the present embodiment.

As can be seen from the polarization state changes in FIG. 22 and fromthe results in FIGS. 23, 24, an optimum retardation value of the opticalcompensating member 16 and an optimum Nz coefficient and optimumretardation value of the optical compensating member 17 depend upon theretardation value of the liquid-crystal layer and upon wavelengthdispersion characteristics of these optical members. In addition, theresults in the o-mode and the results obtained by positionally inversearrangement of the liquid-crystal layer 15 and optical compensatingmember 16 in the optical configuration are substantially the same asobtained in the e-mode.

Fifth Embodiment

A structure of a fifth embodiment is shown in the left of FIG. 1, and anoptical configuration of the e-mode, in FIG. 5. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and another negative “a-plate” is used as an opticalcompensating member 17. This configuration makes it possible to achievethe polarization state changes shown in FIGS. 12A, 12B. A polarizationstate of light which has passed through a transmission axis 11BT of apolarizing layer 11B is denoted by 200T and undergoes a change 416 to bechanged into a polarization state 516 by the optical compensating member16. Next, the polarization state undergoes a change 415 to be changedinto a polarization state 515 by a liquid-crystal layer as if a historyof the change 416 by the optical compensating member 16 were tracedback. The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17. When theretardation value of the optical compensating member 16 is 270 nm andthe retardation value of the optical compensating member 17 is 90 nm, amaximum transmittance of 0.085% and a Δu′v′ value of 0.13 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore applied in the present embodiment.

As can be seen from the polarization state changes in FIGS. 12A, 12B, anoptimum retardation value of the optical compensating member 16 and anoptimum Nz coefficient and optimum retardation value of the opticalcompensating member 17 depend upon the retardation value of theliquid-crystal layer and upon wavelength dispersion characteristics ofthese optical members. In addition, the results in the o-mode and theresults obtained by positionally inverse arrangement of theliquid-crystal layer 15 and optical compensating member 16 in theoptical configuration are substantially the same as obtained in thee-mode.

Sixth Embodiment

A structure of a sixth embodiment is shown in the left of FIG. 1, and anoptical configuration of the e-mode, in FIG. 24. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a positive “c-plate” is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIG. 26. A polarization state oflight which has passed through a transmission axis 11BT of a polarizinglayer 11B is denoted by 200T and undergoes a change 416 to be changedinto a polarization state 516 by the optical compensating member 16.Next, the polarization state undergoes a change 415 to be changed into apolarization state 515 by a liquid-crystal layer 15 as if a history ofthe change 416 by the optical compensating member 16 were traced back.

The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17. When theretardation value of the optical compensating member 16 is 270 nm andthe retardation value of the optical compensating member 17 is 90 nm, amaximum transmittance of 0.085% and a Δu′v′ value of 0.13 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore applied in the present embodiment.

As can be seen from the polarization state changes in FIGS. 12A, 12B, anoptimum retardation value of the optical compensating member 16 and anoptimum Nz coefficient and optimum retardation value of the opticalcompensating member 17 depend upon the retardation value of theliquid-crystal layer and upon wavelength dispersion characteristics ofthese optical members.

In addition, the results in the o-mode and the results obtained bypositionally inverse arrangement of the liquid-crystal layer 15 andoptical compensating member 16 in the optical configuration aresubstantially the same as obtained in the e-mode.

Seventh Embodiment

A structure of a seventh embodiment is shown in the left of FIG. 1, andan optical configuration of the e-mode, in FIG. 21. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical compensating member withan Nz coefficient greater than 1 is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIG. 27. A polarization state oflight which has passed through a transmission axis 11BT of a polarizinglayer 11B is denoted by 200T and undergoes a change 416 to be changedinto a polarization state 516 by the optical compensating member 16.Next, the polarization state undergoes a change 415 to be changed into apolarization state 515 by a liquid-crystal layer 15 as if a history ofthe change 416 by the optical compensating member 16 were traced back.The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17.

Maximum transmittances attained in the present embodiment by changingthe Nz coefficient and retardation value of the optical compensatingmember 17 in a range from 1.5 to 3.5 and a range from 40 to 150 nm,respectively, with the retardation value of the optical compensatingmember 16 fixed at 450 nm, are shown in FIG. 28, and Δu′v′, in FIG. 29.Maximum transmittances of 2% or below are obtained in a retardationrange of 40-120 nm, and favorable viewing-angle characteristics arerealized. In addition, when the Nz coefficient and retardation value ofthe optical compensating member 17 are 1.5 and 60 nm, respectively, amaximum transmittance of 0.11% and a Δu′v′ value of 0.14 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore applied in the present embodiment.

As can be seen from the polarization state changes in FIG. 27 and fromthe results shown in FIGS. 28 and 29, an optimum retardation value ofthe optical compensating member 16 and an optimum Nz coefficient andoptimum retardation value of the optical compensating member 17 dependupon the retardation value of the liquid-crystal layer and uponwavelength dispersion characteristics of these optical members. Inaddition, the results in the o-mode and the results obtained bypositionally inverse arrangement of the liquid-crystal layer 15 andoptical compensating member 16 in the optical configuration aresubstantially the same as obtained in the e-mode.

Eighth Embodiment

A structure of an eighth embodiment is shown in the left of FIG. 1, andan optical configuration of the e-mode, in FIG. 21. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical compensating member withan Nz coefficient greater than 0, but smaller than 1, is used as anoptical compensating member 17. This configuration makes it possible toachieve the polarization state changes shown in FIG. 27. A polarizationstate of light which has passed through a transmission axis 11BT of apolarizing layer 11B is denoted by 200T and undergoes a change 416 to bechanged into a polarization state 516 by the optical compensating member16. Next, the polarization state undergoes a change 415 to be changedinto a polarization state 515 by a liquid-crystal layer as if a historyof the change 416 by the optical compensating member 16 were tracedback. The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17.

Maximum transmittances attained in the present embodiment by changingthe Nz coefficient and retardation value of the optical compensatingmember 17 in a range from 0.1 to 0.9 and a range from 20 to 250 nm,respectively, with the retardation value of the optical compensatingmember 16 fixed at 420 nm, are shown in FIG. 30, and Δu′v′, in FIG. 31.Maximum transmittances of 2% or below are obtained in a retardationrange of 20-220 nm, and favorable viewing-angle characteristics arerealized. In addition, when the Nz coefficient and retardation value ofthe optical compensating member 17 are 0.7 and 130 nm, respectively, amaximum transmittance of 0.088% and a Δu′v′ value of 0.15 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore applied in the present embodiment.

As can be seen from the polarization state changes in FIG. 27 and fromthe results shown in FIGS. 30, 31, an optimum retardation value of theoptical compensating member 16 and an optimum Nz coefficient and optimumretardation value of the optical compensating member 17 depend upon theretardation value of the liquid-crystal layer and upon wavelengthdispersion characteristics of these optical members. In addition, theresults in the o-mode and the results obtained by positionally inversearrangement of the liquid-crystal layer 15 and optical compensatingmember 16 in the optical configuration are substantially the same asobtained in the e-mode.

Ninth Embodiment

A structure of a ninth embodiment is shown in the left of FIG. 1, and anoptical configuration of the e-mode, in FIG. 5. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a biaxially anisotropic optical compensating member withan Nz coefficient greater than 1 is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIG. 32. A polarization state oflight which has passed through a transmission axis 11BT of a polarizinglayer 11B is denoted by 200T and undergoes a change 416 to be changedinto a polarization state 516 by the optical compensating member 16.Next, the polarization state undergoes a change 415 to be changed into apolarization state 515 by a liquid-crystal layer 15 as if a history ofthe change 416 by the optical compensating member 16 were traced back.The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17.

Maximum transmittances attained in the present embodiment by changingthe Nz coefficient and retardation value of the optical compensatingmember 17 in a range from 1.5 to 3.5 and a range from 40 to 250 nm,respectively, with the retardation value of the optical compensatingmember 16 fixed at 580 nm, are shown in FIG. 33, and Δu′v′, in FIG. 34.Maximum transmittances of 2% or below are obtained in a retardationrange of 40-180 nm, and favorable viewing-angle characteristics arerealized. In addition, when the Nz coefficient and retardation value ofthe optical compensating member 17 are 2 and 135 nm, respectively, amaximum transmittance of 0.095% and a Δu′v′ value of 0.14 are attainedand particularly favorable results obtained. This Δu′v′ value istherefore applied in the present embodiment.

As can be seen from the polarization state changes in FIG. 32 and fromthe results shown in FIGS. 33, 34, an optimum retardation value of theoptical compensating member 16 and an optimum Nz coefficient and optimumretardation value of the optical compensating member 17 depend upon theretardation value of the liquid-crystal layer and upon wavelengthdispersion characteristics of these optical members. In addition, theresults in the o-mode and the results obtained by positionally inversearrangement of the liquid-crystal layer 15 and optical compensatingmember 16 in the optical configuration are substantially the same asobtained in the e-mode.

Tenth Embodiment

A structure of a tenth embodiment is shown in the left of FIG. 1, and anoptical configuration of the e-mode, in FIG. 21. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a positive “a-plate” is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIG. 27. A polarization state oflight which has passed through a transmission axis 11BT of a polarizinglayer 11B is denoted by 200T and undergoes a change 416 to be changedinto a polarization state 516 by the optical compensating member 16.Next, the polarization state undergoes a change 415 to be changed into apolarization state 515 by a liquid-crystal layer 15 as if a history ofthe change 416 by the optical compensating member 16 were traced back.The polarization state further undergoes a change 417 into apolarization state 201A by the optical compensating member 17.

When the retardation value of the optical compensating member 16 as aphase-compensating layer is 440 nm, and the retardation value of theoptical compensating member 17 as another phase-compensating layer is 80nm, a maximum transmittance of 0.11% and a Δu′v′ value of 0.12 areattained and particularly favorable results obtained. This Δu′v′ valueis therefore applied in the present embodiment.

As can be seen from the polarization state changes in FIG. 27, anoptimum retardation value of the optical compensating member 16 and anoptimum Nz coefficient and optimum retardation value of the opticalcompensating member 17 depend upon the retardation value of theliquid-crystal layer and upon wavelength dispersion characteristics ofthese optical members. In addition, the results in the o-mode and theresults obtained by positionally inverse arrangement of theliquid-crystal layer 15 and optical compensating member 16 in theoptical configuration are substantially the same as obtained in thee-mode.

Eleventh Embodiment

A structure of an eleventh embodiment is shown in the left of FIG. 1,and an optical configuration of the e-mode, in FIG. 25. In the presentembodiment, a negative “a-plate” is used as an optical compensatingmember 16, and a negative “c-plate” is used as an optical compensatingmember 17. This configuration makes it possible to achieve thepolarization state changes shown in FIG. 35. A polarization state oflight which has passed through a transmission axis 11BT of a polarizinglayer 11B is denoted by 200T and undergoes a change 416 to be changedinto a polarization state 516 by the optical compensating member 16.Next, the polarization state undergoes a change 415 to be changed into apolarization state 515 by a liquid-crystal layer as if a history of thechange 416 by the optical compensating member 16 were traced back. Thepolarization state further undergoes a change 417 into a polarizationstate 201A by the optical compensating member 17.

When the retardation value of the optical compensating member 16 as aphase-compensating layer is 480 nm, and the retardation value of theoptical compensating member 17 as another phase-compensating layer is 80nm, a maximum transmittance of 0.094% and a Δu′v′ value of 0.13 areattained and particularly favorable results obtained. This Δu′v′ valueis therefore applied in the present embodiment.

As can be seen from the polarization state changes in FIG. 27, anoptimum retardation value of the optical compensating member 16 and anoptimum Nz coefficient and optimum retardation value of the opticalcompensating member 17 depend upon the retardation value of theliquid-crystal layer and upon wavelength dispersion characteristics ofthese optical members. In addition, the results in the o-mode and theresults obtained by positionally inverse arrangement of theliquid-crystal layer 15 and optical compensating member 16 in theoptical configuration are substantially the same as obtained in thee-mode.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

1. A liquid crystal display device comprising: a first substrate with afirst polarizing layer at an incident side of light; a second substratewith a second polarizing layer which includes an absorption axis suchthat the smaller of two angles formed with respect to the absorptionaxis of the first polarizing layer ranges from 88° to 90°; aliquid-crystal layer on which liquid-crystal molecules are oriented suchthat the smaller of two angles formed with respect to the firstsubstrate or the second substrate ranges from 0° to 5°, and such thatthe smaller of two angles formed with respect to the absorption axis ofthe first polarizing layer ranges from 88° to 90° or the smaller of twoangles formed ranges from 0° to 2°; a matrix-driven electrode group withone pair of electrodes arranged on a pixel-by-pixel basis at a sideclose to the liquid-crystal layer, on either the first substrate or thesecond substrate; and a rear-illuminating device; wherein: between theliquid-crystal layer and at least one of the first polarizing layer andthe second polarizing layer, a first optical compensating member isdisposed without a birefringent medium sandwiched between theliquid-crystal layer and the first optical compensating member; thefirst optical compensating member is constructed so that when arefractive index thereof in a slow-axis direction in a plane parallel tothe substrate is taken as n1, a refractive index in a fast-axisdirection in the plane parallel to the substrate is taken as n2, and arefractive index in a thickness direction is taken as n3, the firstoptical compensating member satisfies n1≈n3>n2; a slow axis of the firstoptical compensating member in the plane parallel to the substrate has apredetermined relationship with respect to an optical axis of theliquid-crystal layer; color filters for an N number of colors (N≧2) areprovided on the first substrate or the second substrate; and whenwavelengths that denote maximum transmittance values of the colorfilters are each expressed as λ_(M) (M=1, 2, etc., up to N) in orderwith the shortest of the wavelengths first, if a difference between anextraordinary-light refractive index and ordinary-light refractive indexat the λ_(M) of the liquid-crystal layer that is associated with thecolor filter having the wavelength λ_(M) which denotes one of themaximum transmittance values, is taken as ΔnLC(λ_(M)), and thickness, asdLC_(M), and a refractive index in the slow-axis direction in a planeparallel to the associated substrate, at the λ_(M) of the first opticalcompensating member that is associated with the color filter having thewavelength λ_(M) which denotes one of the maximum transmittance values,is taken as n1(λ_(M)), a refractive index in the fast-axis direction inthe substrate parallel plane is taken as n2(λ_(M)), and thickness istaken as dr_(M),|ΔnLC(λ_(M-1))·dLC _(M-1)−(n1(λ_(M-1))−n2(λ_(M-1)))·dr _(M-1)|/|ΔnLC(λ_(M))·dLC _(M)−(n1(λ_(M))−n2(λ_(M)))·dr _(M)|<(0.9+0.04/λ_(M-1) ²+0.0008/λ_(M-1) ⁴)/(0.9+0.04/λ_(M) ²+0.0008/λ_(M) ⁴) issatisfied for all M′s (M=1, 2, etc., up to N).
 2. The liquid crystaldisplay device according to claim 1, wherein: when wavelengths thatdenote maximum transmittance values of the color filters are eachexpressed as λ_(M)(M=1, 2, etc., up to N) in order with the shortest ofthe wavelengths first, if thickness of the liquid-crystal layer that isassociated with the color filter having the wavelength λ_(M) thereofthat denotes one of the maximum transmittance values, is taken asdLC_(M): at least in a case of M=K(2≦K≦N),dLC _(K) >dLC _(K−1) is satisfied; and in cases of M being other than K,dLC _(M) ≧dLC _(M−1) is satisfied.
 3. The liquid crystal display deviceaccording to claim 2, wherein: when thicknesses of the liquid-crystallayer that are associated with red, green, and blue pixels of the colorfilters are expressed as dLC_(R), dLC_(G), and dLC_(B), respectively,dLC_(R ≧dLC) _(G >dLC) _(B) is satisfied.
 4. The liquid crystal displaydevice according to claim 1, wherein: the first optical compensatingmember is disposed without a birefringent medium sandwiched between theliquid-crystal layer and the first polarizing layer.
 5. The liquidcrystal display device according to claim 1, wherein: the first opticalcompensating member is disposed without a birefringent medium sandwichedbetween the liquid-crystal layer and the second polarizing layer.
 6. Theliquid crystal display device according to claim 1, wherein: the opticalaxis of the liquid-crystal layer is substantially vertical to anabsorption axis of the first polarizing layer; and a second opticalcompensating member is disposed between the second polarizing layer andthe liquid-crystal layer.
 7. The liquid crystal display device accordingto claim 6, wherein: if a wavelength of incident light is 550 nm, adifference between an extraordinary-light refractive index of theliquid-crystal layer and an ordinary-light refractive index thereof isexpressed as ΔnLC, and a cell gap is expressed as dLC, and when therefractive index of the first optical compensating member in theslow-axis direction thereof in a plane parallel to the associatedsubstrate is taken as n1, the refractive index of the first opticalcompensating member in the fast-axis direction thereof in the substrateparallel plane is taken as n2, and thickness of the first opticalcompensating member is taken as dr,0 nm<ΔnLC·dLC−(n1−n2)·dr<275 nm is satisfied; when a refractive index ofthe second optical compensating member in a slow-axis direction thereofin the substrate parallel plane is taken as n1, a refractive index ofthe second optical compensating member in a fast-axis direction thereofin the substrate parallel plane is taken as n2, and a refractive indexof the second optical compensating member in a thickness directionthereof is taken as n3,(n1−n3)/(n1−n2)<1 is satisfied; and a slow axis of the second opticalcompensating member in the substrate parallel plane is substantiallyparallel to the optical axis of the liquid-crystal layer.
 8. The liquidcrystal display device according to claim 7, wherein: the second opticalcompensating member satisfies n1≈n3>n2.
 9. The liquid crystal displaydevice according to claim 7, wherein: if the wavelength of the incidentlight is 550 nm, when a refractive index of the second opticalcompensating member in a slow-axis direction thereof in a plane parallelto the associated substrate is taken as n1, a refractive index of thesecond optical compensating member in a fast-axis direction thereof inthe substrate parallel plane is taken as n2, a refractive index of thesecond optical compensating member in a thickness direction thereof istaken as n3, and thickness of the second optical compensating member istaken as dr,0<(n1−n3)/(n1−n2)<1and(n1−n2)*dr<100 nm are satisfied.
 10. The liquid crystal display deviceaccording to claim 7, wherein: if the wavelength of the incident lightis 550 nm, when a refractive index of the second optical compensatingmember in a slow-axis direction thereof in a plane parallel to theassociated substrate is taken as n1, a refractive index of the secondoptical compensating member in a fast-axis direction thereof in thesubstrate parallel plane is taken as n2, a refractive index of thesecond optical compensating member in a thickness direction thereof istaken as n3, and thickness of the second optical compensating member istaken as dr,(n1−n3)/(n1−n2)<0and−150 nm<((n1+n2)/2−n3)*dr<0 nm are satisfied.
 11. The liquid crystaldisplay device according to claim 6, wherein: if a wavelength ofincident light is 550 nm, a difference between an extraordinary-lightrefractive index of the liquid-crystal layer and an ordinary-lightrefractive index thereof is expressed as ΔnLC, and a cell gap isexpressed as dLC, and when the refractive index of the first opticalcompensating member in the slow-axis direction thereof in the substrateparallel plane is taken as n1, the refractive index of the first opticalcompensating member in the fast-axis direction thereof in the substrateparallel plane is taken as n2, and thickness of the first opticalcompensating member is taken as dr,0 nm<ΔnLC·dLC−(n1−n2)·dr<275 nm is satisfied; when a refractive index ofthe second optical compensating member in a slow-axis direction thereofin a plane parallel to the associated substrate is taken as n1, arefractive index of the second optical compensating member in afast-axis direction thereof in the substrate parallel plane is taken asn2, and a refractive index of the second optical compensating member ina thickness direction thereof is taken as n3, (n1−n3)/(n1−n2)<0 issatisfied; and a slow axis of the second optical compensating member inthe substrate parallel plane is substantially vertical to the opticalaxis of the liquid-crystal layer.
 12. The liquid crystal display deviceaccording to claim 6, wherein: if a wavelength of incident light is 550nm, a difference between an extraordinary-light refractive index of theliquid-crystal layer and an ordinary-light refractive index thereof isexpressed as ΔnLC, and a cell gap is expressed as dLC, and when therefractive index of the first optical compensating member in theslow-axis direction thereof in a plane parallel to the associatedsubstrate is taken as n1, the refractive index of the first opticalcompensating member in the fast-axis direction thereof in the substrateparallel plane is taken as n2, and thickness of the first opticalcompensating member is taken as dr,−275 nm <ΔnLC·dLC−(n1−n2)·dr<0 nm is satisfied; when a refractive indexof the second optical compensating member in a slow-axis directionthereof in the substrate parallel plane is taken as n1, a refractiveindex of the second optical compensating member in a fast-axis directionthereof in the substrate parallel plane is taken as n2, and a refractiveindex of the second optical compensating member in a thickness directionthereof is taken as n3,(n1−n3)/(n1−n2)>0 is satisfied; and a slow axis of the second opticalcompensating member in the substrate parallel plane is substantiallyvertical to the optical axis of the liquid-crystal layer.
 13. The liquidcrystal display device according to claim 12, wherein: the secondoptical compensating member satisfies n1>n2≈n3.
 14. The liquid crystaldisplay device according to claim 12, wherein: if the wavelength of theincident light is 550 nm, when the refractive index of the secondoptical compensating member in the slow-axis direction thereof in theplane parallel to the associated substrate is taken as n1, therefractive index of the second optical compensating member in thefast-axis direction thereof in the substrate parallel plane is taken asn2, the refractive index of the second optical compensating member inthe thickness direction thereof is taken as n3, and the thickness of thesecond optical compensating member is taken as dr,0<(n1−n3)/(n1−n2)<1and(n1−n2)*dr<100 nm are satisfied.
 15. The liquid crystal display deviceaccording to claim 12, wherein: if the wavelength of the incident lightis 550 nm, when the refractive index of the second optical compensatingmember in the slow-axis direction thereof in the plane parallel to theassociated substrate is taken as n1, the refractive index of the secondoptical compensating member in the fast-axis direction thereof in thesubstrate parallel plane is taken as n2, the refractive index of thesecond optical compensating member in the thickness direction thereof istaken as n3, and the thickness of the second optical compensating memberis taken as dr,(n1−n3)/(n1−n2)>1and0 nm<((n1+n2)/2−n3)*dr<150 nm are satisfied.
 16. The liquid crystaldisplay device according to claim 6, wherein: if a wavelength ofincident light is 550 nm, a difference between an extraordinary-lightrefractive index of the liquid-crystal layer and an ordinary-lightrefractive index thereof is expressed as ΔnLC, and a cell gap isexpressed as dLC, and when the refractive index of the first opticalcompensating member in the slow-axis direction thereof in a planeparallel to the associated substrate is taken as n1, the refractiveindex of the first optical compensating member in the fast-axisdirection thereof in the substrate parallel plane is taken as n2, andthickness of the first optical compensating member is taken as dr,−275nm<ΔnLC·dLC−(n1−n2)·dr<0 nm is satisfied; when a refractive index ofthe second optical compensating member in a slow-axis direction thereofin the substrate parallel plane is taken as n1, a refractive index ofthe second optical compensating member in a fast-axis direction thereofin the substrate parallel plane is taken as n2, and a refractive indexof the second optical compensating member in a thickness directionthereof is taken as n3,(n1−n3)/(n1−n2)>1 is satisfied; and a slow axis of the second opticalcompensating member in the substrate parallel plane is substantiallyparallel to the optical axis of the liquid-crystal layer.
 17. The liquidcrystal display device according to claim 1, wherein: the optical axisof the liquid-crystal layer is substantially parallel to an absorptionaxis of the first polarizing layer; and a second optical compensatingmember is disposed between the first polarizing layer and theliquid-crystal layer.
 18. The liquid crystal display device according toclaim 1, wherein the first optical compensating member is disposedbetween the first polarizing layer and the liquid-crystal layer.